On common objective of designers and manufacturers of displays using cathode ray tubes (CRTs) is to reduce glare resulting from the reflection of ambient light off of the CRT face. Several approaches have been used to reduce such glare. In one approach, the surface of a CRT screen is treated by chemical etching such as by means of a hydrofluoric acid solution. In another approach, an anti-glare filter is used that consists of a piece of glass or other material having an anti-reflective view surface. In this approach, the filter is placed in a frame and suspended in front of the CRT view surface.
The preferred approach, however, is to apply optical interference coatings directly to a CRT screen. This can be done through a variety of thin film deposition techniques such as electron beam deposition, chemical vapor deposition, among others. One reason direction application of optical interference coatings is preferred is that is possible for the anti-reflective coating to be electrically conductive. Electrical conductivity facilitates the dissipation of static electrical charges and thereby reduces accumulation of dust on the CRT. Electrically conductive coatings, when effectively grounded, also substantially reduce the ELf/VLF field emissions from the CRT.
One the optical interference coating is applied, it is desirable to evaluate the uniformity or quality of the coating. However, the coating is usually elevated in temperature, so any object coming in contact with the coating before the coating has cooled will disrupt the coating. For example, if contact with the coating is made by an organize compound (e.g., plastic), the compound will leave undesirable reside on the coating. If contact is made by a metallic object, the object may scratch the coating. Thus, in the past, it has been necessary to wait until the coating completely settles and/or cools before it is tested. This delay complicates the manufacturing process, and therefore increases the cost of coating the CRT displays. Accordingly, there exists a need for a system or method for evaluating the quality of a thin film coating soon after the coating is applied to a CRT display.
In addition, experience has shown that when a number of CRTs are coated in succession (e.g., in an assembly line), the thickness or uniformity of the layers applied to each CRT tends to vary among CRTs. Because the quality of the anti-reflective coating depends on the thickness of the layers of material, this variance diminishes the quality of the anti-reflective coating. Accordingly, there exists a need not only to evaluate the coating applied to CRTs to determine whether quality is diminishing, but also to maintain a consistent high-quality anti-reflective coating.
These and other deficiencies in the art that are addresses by the present invention will become apparent upon reading the following detailed description in the context of the associated drawings.